139 lines
3.9 KiB
Go
139 lines
3.9 KiB
Go
// Copyright 2015 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package buffer
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import (
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"fmt"
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"log"
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"reflect"
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"unsafe"
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"github.com/jacobsa/fuse/internal/fusekernel"
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)
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const outHeaderSize = unsafe.Sizeof(fusekernel.OutHeader{})
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// OutMessage structs begin life with Len() == OutMessageInitialSize.
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const OutMessageInitialSize = outHeaderSize
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// We size out messages to be large enough to hold a header for the response
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// plus the largest read that may come in.
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const outMessageSize = outHeaderSize + MaxReadSize
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// OutMessage provides a mechanism for constructing a single contiguous fuse
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// message from multiple segments, where the first segment is always a
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// fusekernel.OutHeader message.
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//
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// Must be initialized with Reset.
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type OutMessage struct {
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offset uintptr
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storage [outMessageSize]byte
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}
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// Make sure alignment works out correctly, at least for the header.
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func init() {
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a := unsafe.Alignof(OutMessage{})
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o := unsafe.Offsetof(OutMessage{}.storage)
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e := unsafe.Alignof(fusekernel.OutHeader{})
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if a%e != 0 || o%e != 0 {
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log.Panicf("Bad alignment or offset: %d, %d, need %d", a, o, e)
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}
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}
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// Reset the message so that it is ready to be used again. Afterward, the
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// contents are solely a zeroed header.
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func (m *OutMessage) Reset() {
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m.offset = OutMessageInitialSize
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memclr(unsafe.Pointer(&m.storage), OutMessageInitialSize)
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}
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// Return a pointer to the header at the start of the message.
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func (b *OutMessage) OutHeader() (h *fusekernel.OutHeader) {
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h = (*fusekernel.OutHeader)(unsafe.Pointer(&b.storage))
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return
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}
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// Grow the buffer by the supplied number of bytes, returning a pointer to the
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// start of the new segment, which is zeroed. If there is no space left, return
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// the nil pointer.
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func (b *OutMessage) Grow(size uintptr) (p unsafe.Pointer) {
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p = b.GrowNoZero(size)
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if p != nil {
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memclr(p, size)
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}
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return
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}
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// Equivalent to Grow, except the new segment is not zeroed. Use with caution!
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func (b *OutMessage) GrowNoZero(size uintptr) (p unsafe.Pointer) {
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if outMessageSize-b.offset < size {
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return
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}
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p = unsafe.Pointer(uintptr(unsafe.Pointer(&b.storage)) + b.offset)
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b.offset += size
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return
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}
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// Throw away the last n bytes. Panics if n is out of range.
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func (b *OutMessage) Shrink(n uintptr) {
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if n > b.offset-OutMessageInitialSize {
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panic(fmt.Sprintf("Shrink(%d) out of range for offset %d", n, b.offset))
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}
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b.offset -= n
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}
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// Equivalent to growing by the length of p, then copying p over the new
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// segment. Panics if there is not enough room available.
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func (b *OutMessage) Append(src []byte) {
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p := b.GrowNoZero(uintptr(len(src)))
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if p == nil {
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panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
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}
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sh := (*reflect.SliceHeader)(unsafe.Pointer(&src))
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memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
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return
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}
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// Equivalent to growing by the length of s, then copying s over the new
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// segment. Panics if there is not enough room available.
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func (b *OutMessage) AppendString(src string) {
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p := b.GrowNoZero(uintptr(len(src)))
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if p == nil {
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panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
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}
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sh := (*reflect.StringHeader)(unsafe.Pointer(&src))
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memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
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return
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}
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// Return the current size of the buffer.
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func (b *OutMessage) Len() int {
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return int(b.offset)
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}
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// Return a reference to the current contents of the buffer.
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func (b *OutMessage) Bytes() []byte {
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return b.storage[:int(b.offset)]
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}
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